Onions Made Pre-Human Ancestors Cry Too, Study Suggests

The sensors in your body that make you tear up when you're cutting onions have been around for 500 million years, a new study finds.

Foods like wasabi and onions, as well as substances like tear gas and cigarette smoke, contain tissue-damaging and irritating chemicals. When you get a taste or waft of the substances, a protein found throughout your body is thought to sense these irritating chemicals and send signals to your nervous system. The result is pain, which is why slicing onions makes you cry.

In the new study, scientists found this chemical-sensing protein, called TRAPA1, is present in flies and for exactly the same purpose. Even more surprising, the team thinks the protein could date back millions of years to the common ancestor of all the varied creatures in the animal kingdom.

During the Cambrian Period, which lasted from 543 million to 490 million years ago, life forms included primitive marine organisms, such as echinoderms (a group that now includes sea stars and sea cucumbers), annelid worms and sponge-like organisms.

Garrity and his colleagues reconstructed TRPA1's family tree back some 700 million years using a variety of bioinformatic methods (bioinformactics applies computer programs and statistic techniques to study biological data).

For instance, the researchers compared the TRPA1 protein from different organisms to see how similar they were. They then used several computer programs to figure out how the proteins would relate to each other in terms of evolution.